1. Field
This disclosure relates to an arrangement method of superconducting wires of a superconducting cable, and more particularly, to an arrangement method of superconducting wires of a superconducting cable capable of suitably determining the number of superconducting wires while maintaining a current-carrying capability depending on a temperature deviation of sections of the superconducting cable including the superconducting wires for arrangement of the superconducting wires.
2. Description of the Related Art
Superconducting cables are recently spotlighted as high-density current transmission cables which use properties of superconducting wires in which the resistance drops abruptly at a low temperature (substantially 100K or less in a high-temperature superconductor, and substantially 20K or less in a low-temperature superconductor) and approaches zero.
In such superconducting cables, high-temperature superconducting cables can be easily obtained and maintain superconducting properties using liquid nitrogen which is cheap, and thus they are developed to a significant level. In embodiments of this disclosure, such high-temperature superconducting cables are applied and described.
As illustrated in FIG. 1, a superconducting cable system includes two terminal structures 20 and 30 to which superconducting cable 10 (a line represented as a shaded part in FIG. 1) is connected and a refrigerator 40 provided on the front side of the one terminal structure 20.
The superconducting cable 10 according to the related art is typically manufactured to have a length of 600 m for use. In order to extend the length as needed, a plurality of intermediate pull boxes 11, 12, and 13 are connected.
Moreover, in the superconducting cable system according to the related art, a cooling flow path (a flow path formed between an inner can and an outer can of a vacuum layer and the like) through which a cooling fluid (for example, liquid nitrogen) flows is provided in the superconducting cable 10. In addition, the superconducting cable system is configured to supply the cooling fluid through the one terminal structure 20, discharge the cooling fluid through the other terminal structure 30 to be recovered by a recovery pipe 50, and supply the cooling fluid to the refrigerator 40 again.
Moreover, a pump 42 is installed between the refrigerator 40 and the terminal structure 20 to circulate the cooling fluid through the superconducting cable 10 and the recovery pipe 50.
The superconducting cable 10 is configured of superconducting wires that form a core as conductors. In a case where the superconducting cable 10 has a short length of 600 m, a temperature deviation of sections of the superconducting cable 10 rarely occurs, and thus the same number of superconducting wires is used through the sections.
The superconducting wire has properties of increasing the current-carrying capability when the temperature decreases and decreasing the current-carrying capability when the temperature increases. In general, it is known that the current-carrying capability increases by 8% when the temperature decreases by 1° C.
Therefore, as shown in FIG. 1, for a long distance, in a case where the superconducting cable 10 has a great length (for example, 3,200 m), the temperature of an inlet portion 10a of the superconducting cable 10 connected to the terminal structure 20 provided on the side where the refrigerator 40 is provided is low, and the temperature of an outlet portion 10b of the superconducting cable 10 connected to the terminal structure 30 on the opposite side increases due to heat invasion and heat generated by the conductors as the cooling fluid passes through the superconducting cable 10, resulting in a temperature deviation of sections.
In the superconducting cable 10 according to the related art, depending to a correlation between the superconducting wire and the temperature, the number of superconducting wires is determined by calculating current that the superconducting wires can transmit on the basis of the temperature of the cable side of a section with the lowest current-carrying capability (a section with the highest temperature). Over the entire sections of the superconducting cable for a long distance, similarly to the superconducting cable for a short distance, the same number of superconducting wires is used through the sections.
In other words, the number of superconducting wires that is determined on the basis of the temperature of the cable side of the section on the terminal structure 30 side, which has the highest temperature, is applied through all the sections L1, L2, L3, and L4.
For more specific description, an operation of determining the number of superconducting wires will be described in detail with reference to Table 1 as follows.
TABLE 1Temperature (K)IC Current (A)77907697.275104.97674113.374173122.44472132.239571142.818770154.244268166.583767179.910466194.303265209.8475
Table 1 shows values calculated through a simulation with temperature on a superconducting wire in a case where the temperature of liquid nitrogen which is a cooling fluid in the atmosphere is 77 K and an IC current is 90 A at this time.
With regard to the performance of the superconducting cable system described with reference to FIG. 1, the length of the superconducting cable 10 is 3,200 m, the carried current is 14,000 A, the temperature of the inlet portion 10a is 65K, and the temperature of the outlet portion 10b is 72K.
In addition, with regard to the temperature of each section of the superconducting cable 10, the temperature of the section L1 (an interval of 800 m from the inlet portion 10a to the intermediate pull box 11) is 66.5K, the temperature of the section L2 (at 1,600 m position from the inlet portion 10a) is 68.5K, the temperature of the section L3 (at 2,400 m position from the inlet portion 10a) is 70.2K, and the temperature of the section L4 (at 3,200 m position from the inlet portion 10a) is 72K.
Therefore, the number of superconducting wires needed for the superconducting cable system according to the related art is as follows.
The number of wires=14,000/132.2395 (the amount of current of a strand of wire at 72K)=105.87, substantially 106 strands are needed.
As shown in FIG. 1, when the number of superconducting wires of the section L4 having the highest temperature is determined as 106 strands, the numbers of superconducting wires of the other sections L1, L2, and L3 are determined as 106 strands.
Consequently, since the numbers of superconducting wires are determined on the basis of the section having the highest temperature, even though the temperature decreases as being closer to the inlet portion 10a of the superconducting cable 10 which has the lowest temperature, the superconducting wires having more strands than necessary are used. The superconducting wires are important to the manufacturing cost of the superconducting cable 10 and thus become causes of an increase in the total cost of the superconducting cable 10. Moreover, there is a problem in that a superconductor connection time is unnecessarily increased due to the more number of superconducting wires than necessary, resulting in degradation of operability.